.content {
    width: 640px;
    height: 640px;
    margin: 0 auto;
    position: relative;
}

.btn {
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0;
    top: 0;
    background: rgba(0, 0, 0, .3);
    z-index: 2;
}

.btn button {
    background: none;
    border: none;
    background-size: 100% 100%;
    cursor: pointer;
    outline: none;
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

.startBtn button {
    width: 250px;
    height: 200px;
    background-image: url(./imgs/button.png);
    opacity: .8;
}

.pauseBtn {
    display: none;
}

.pauseBtn button {
    width: 100px;
    height: 100px;
    background-image: url(./imgs/pause.png);
}

#snakeWrap {
    position: relative;
    width: 600px;
    height: 600px;
    background-color: #bbc4b0;
    border: 20px solid #d1e9b7;
}

.snakeHead {
    background-image: url(./imgs/snake.png);
    background-size: cover;
}

.snakeBody {
    background-color: #12663f;
    border-radius: 50%;
}

.food {
    background-image: url(./imgs/food.png);
    background-size: cover;
}

ul {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    width: 60vw;
    height: 60vw;
    margin-left: auto;
    margin-right: auto;
    position: relative;
}

ul#control li {
    box-sizing: border-box;
    list-style: none;
    margin: 0;
    padding: 0;
    padding: 6px 0;
    background-color: gray;
    width: 20vw;
    height: 20vw;
    position: absolute;
    color: white;
    font-weight: bold;
    font-size: 30px;
    text-align: center;
    cursor: pointer;
    border: white 1px solid;
    transform: rotateZ(45deg);
}

.l1 {
    left: 20vw;
    top: 5vw;
    border-radius: 50% 0 0 0;
}

.l2 {
    left: 35vw;
    top: 20vw;
    border-radius: 0 50% 0 0;
}

.l3 {
    left: 20vw;
    top: 35vw;
    border-radius: 0 0 50% 0;
}

.l4 {
    left: 5vw;
    top: 20vw;
    border-radius: 0 0 0 50%;
}

.fast,
.slow {
    /* z-index: 2; */
    display: inline-block;
    text-align: center;
    /* float: left; */
    position: relative;
    /* width: 200px; */
    left: 10px;
}

.fast button,
.slow button {
    width: 150px;
}

@media screen and (max-width:500px) {
    * {
        margin: 0;
        padding: 0;
    }
    /*
    .content {
        width: 100vw;
        height: 100vw;
    }
*/
    body {
        position: relative;
    }
    .content {
        width: 320px;
        height: 320px;
        /*        position: absolute;*/
        /*        left: 50%;*/
        /*        transform: translate(-50%, 0);*/
    }
    #snakeWrap {
        border: 10px solid #d0e7f1;
        width: 300px;
        height: 300px;
    }
}